The present invention relates to a photothermographic material. In particular, the present invention relates to a photothermographic material showing little fog and little sensitivity fluctuation during storage before light exposure as a photothermographic material for laser imagers.
In the medical field and the field of printing plate making, waste solutions generated with wet processing of image-forming materials have conventionally caused a problem concerning workability, and in recent years, it is strongly desired to reduce the amount of the processing waste solutions also from the standpoints of environmental protection and space saving. Therefore, techniques relating to photothermographic materials that can be efficiently exposed by using laser imagers and can form clear black images with high resolution and sharpness have been noted.
As such techniques, there are known, for example, photothermographic materials containing a silver salt of an organic acid, photosensitive silver halide grains, a reducing agent and a binder on a support, as described in U.S. Pat. Nos. 3,152,904, 3,457,075, D. Morgan, xe2x80x9cDry Silver Photographic Materialsxe2x80x9d in Handbook of Imaging Materials, Marcel Dekker, Inc., page 48, 1991 and so forth.
However, since photothermographic materials contain all the materials for development within the photosensitive materials, they suffer from a drawback that storability before development is markedly poorer compared with photosensitive materials for wet processing.
For use in photomechanical processes for printing, a substantially colorless photosensitive material (in particular, colorless for the UV region) that can provide high contrast photographic characteristic is required. In a photosensitive material for which exposure with an infrared ray is intended, absorption in the visible region of sensitizing dyes and antihalation dyes can be markedly reduced and hence a substantially colorless photosensitive material can easily be produced. Thus, techniques concerning infrared sensitive photothermographic silver halide photographic materials have been developed. Spectral sensitization techniques are disclosed in Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) No. 3-10391, JP-B-6-52387, Japanese Patent Laid-open Publication (Kokai, henceforth referred to as JP-A) No. 5-341432, JP-A-6-194781, JP-A-6-301141 and so forth, and antihalation techniques are disclosed in JP-A-7-13295, U.S. Pat. No. 5,380,635 and so forth. Furthermore, as for methods of obtaining high contrast photographic characteristic, European Patent Publication (hereinafter referred to as EP-A) 762,196, JP-A-9-90550 and so forth disclose that high-contrast photographic characteristic can be obtained by incorporating Group VII or VIII metal ions or metal complex ions thereof into photosensitive silver halide grains for use in photothermographic materials, or incorporating a hydrazine derivative into the photothermographic materials.
Meanwhile, photosensitive materials for platemaking are used as intermediate materials in printing process, i.e., as masks for producing printing plates. In recent years, digitization and automation of operations have been widely diffused for the whole printing process, and light exposure and development of PS plates in the platemaking process are automated by the use of platemaking machines. Such platemaking machines serve as systems that operate when information required for automatic transportation, automatic light exposure and so forth (bar code or register mark) written on photothermographic materials is read by sensors of the platemaking machines. These sensors utilize laser diodes of a wavelength around 670 nm. That is, it is indispensable that the information written on the photothermographic materials can be read at a wavelength of 670 nm, and it is preferred that the photothermographic materials should show low Dmin (minimum density) at a wavelength of around 670 nm. In particular, it is preferable to use an antihalation dye showing low absorption in the visible region.
However, dyes providing spectral sensitization by infrared absorption generally show high HOMO and hence strong reducing ability, and thus they are likely to reduce silver ions in photothermographic materials to degrade fog of the photothermographic materials. In particular, during storage under high temperature and high humidity or storage for a long period of time, marked change of performance may be observed. Moreover, if a dye showing low HOMO is used in order to prevent the degradation of storability, LUMO also correspondingly becomes lower. Thus, spectral sensitization efficiency is reduced and hence sensitivity is lowered. These problems concerning sensitivity, storability and performance fluctuation are observed not only in wet type photosensitive materials, but also in photothermographic materials, in which the problems become more serious.
As for photothermographic materials utilizing silver iodide (AgI), methods of using AgI formed by conversion of a silver salt of an organic acid are disclosed in U.S. Pat. No. 6,143,488, EP-A-922,995, International Patent Publications WO97/48014, WO97/48015, U.S. Pat. No. 6,165,705, JP-A-8-297345, Japanese Patent No. 2,785,129 and so forth. However, any of these cannot achieve sensitivity and fog of sufficient levels.
Therefore, there have been desired techniques for providing photothermographic materials that can provide images with low fog as well as little increase of fog and little sensitivity fluctuation during storage before light exposure, and are advantageous for environment and cost.
Therefore, a first object to be achieved by the present invention is to provide a photothermographic material, in particular for laser imagers, that shows low fog, little increase of fog and little sensitivity fluctuation during storage before light exposure.
The inventor of the present invention assiduously studied, and as a result, found that a superior photothermographic material could be obtained by utilizing silver halide grains of high silver iodide content and silver halide grains of low silver iodide content in combination. Thus, the present invention was accomplished.
That is, the present invention provides a photothermographic material containing a silver salt of an organic acid, a silver halide and a reducing agent on a transparent support, which has two or more maximum values of silver content in silver iodide content distribution of total silver halide grains contained in the photothermographic material plotted with silver iodide content in abscissa and silver content in silver halide grains in ordinate, wherein at least one maximum value is in a silver iodide content range of less than 10 mol % and at least one maximum value is in a silver iodide content range of 10 mol % or more.
The photothermographic material of the present invention preferably satisfies the requirement defined by the following equation (1):                                                                                                                                                                                       Total                          ⁢                                                      xe2x80x83                                                    ⁢                          amount                          ⁢                                                      xe2x80x83                                                    ⁢                          of                          ⁢                                                      xe2x80x83                                                    ⁢                          silver                          ⁢                                                      xe2x80x83                                                    ⁢                          contained                                                                                                                                                              in                          ⁢                                                      xe2x80x83                                                    ⁢                          silver                          ⁢                                                      xe2x80x83                                                    ⁢                          halide                          ⁢                                                      xe2x80x83                                                    ⁢                          having                          ⁢                                                      xe2x80x83                                                    ⁢                          silver                                                                                                                                                                                      iodide                    ⁢                                          xe2x80x83                                        ⁢                    content                    ⁢                                          xe2x80x83                                        ⁢                    of                    ⁢                                          xe2x80x83                                        ⁢                    less                    ⁢                                          xe2x80x83                                        ⁢                    than                    ⁢                                          xe2x80x83                                        ⁢                    10                    ⁢                                          xe2x80x83                                        ⁢                    mol                    ⁢                                          xe2x80x83                                        ⁢                    %                                                                                                                                            Total                    ⁢                                          xe2x80x83                                        ⁢                    amount                    ⁢                                          xe2x80x83                                        ⁢                    of                    ⁢                                          xe2x80x83                                        ⁢                    silver                    ⁢                                          xe2x80x83                                        ⁢                    contained                                                                                                                                                                                            in                          ⁢                                                      xe2x80x83                                                    ⁢                          silver                          ⁢                                                      xe2x80x83                                                    ⁢                          halide                          ⁢                                                      xe2x80x83                                                    ⁢                          having                          ⁢                                                      xe2x80x83                                                    ⁢                          silver                                                                                                                                                              iodide                          ⁢                                                      xe2x80x83                                                    ⁢                          content                          ⁢                                                      xe2x80x83                                                    ⁢                          of                          ⁢                                                      xe2x80x83                                                    ⁢                          10                          ⁢                                                      xe2x80x83                                                    ⁢                          mol                          ⁢                                                      xe2x80x83                                                    ⁢                          %                          ⁢                                                      xe2x80x83                                                    ⁢                          or                          ⁢                                                      xe2x80x83                                                    ⁢                          more                                                                                                                                                  xc3x97          100                ≧                                                            Average                ⁢                                  xe2x80x83                                ⁢                silver                ⁢                                  xe2x80x83                                ⁢                iodide                ⁢                                  xe2x80x83                                ⁢                content                                                                                                                                                    of                      ⁢                                              xe2x80x83                                            ⁢                      silver                      ⁢                                              xe2x80x83                                            ⁢                      halide                      ⁢                                              xe2x80x83                                            ⁢                      having                      ⁢                                              xe2x80x83                                            ⁢                      silver                                                                                                                                  iodide                      ⁢                                              xe2x80x83                                            ⁢                      content                      ⁢                                              xe2x80x83                                            ⁢                      of                      ⁢                                              xe2x80x83                                            ⁢                      10                      ⁢                                              xe2x80x83                                            ⁢                      mol                      ⁢                                              xe2x80x83                                            ⁢                      %                      ⁢                                              xe2x80x83                                            ⁢                      or                      ⁢                                              xe2x80x83                                            ⁢                      more                                                                                                                              Equation        ⁢                  xe2x80x83                ⁢                  (          1          )                    
Further, the silver halide having a silver iodide content of less than 10 mol % is preferably a photosensitive silver halide. Furthermore, in the photothermographic material of the present invention, the silver halide having a silver iodide content of less than 10 mol % preferably has an average silver iodide content of 5 mol % or less, and the silver halide having a silver iodide content of 10 mol % or more preferably has an average silver iodide content of 30 mol % or more. Further, the photothermographic material of the present invention preferably contains a high contrast agent.
According to the present invention, there can be provided a photothermographic material that shows low fog, little increase of fog and little sensitivity fluctuation during storage before light exposure. The photothermographic material of the present invention can be used for purposes of a wide range including use in laser imagers.